A massive coordinated attack was launched in Mumbai, India just hours after the FBI warned that Al Qaeda may be targeting New York's subways and railroads.

If Al Qaeda terrorists have their way there will be chaos and mayhem here this holiday season, a mass transit bomb plot that would probably affect all the subway and train lines at Penn and Grand Central stations.

"The threat is serious, the threat is significant, and it is plausible," said Congressman Peter King, R-Long Island, a member of the House Homeland Security Committee.

Uniformed officers, including this NYPD Counter Terrorism Squad members and Amtrak cops with M-16s, flooded Penn Station Wednesday after the FBI said it had received a "plausible but unsubstantiated" report that Al Qaeda operatives discussed a plan two months ago to bomb New York City's mass transit system.

The report said: "These discussions reportedly involved the use of suicide bombers or explosives placed on subway/passenger rail systems."

Sources told CBS 2 HD the plot involved the Long Island Rail Road. If the explosion went off in Penn Station, the source said, it would affect transportation of Amtrak's northeast corridor between Boston and Washington, LIRR service and New York City subway service.

"This is definitely linked to Al Qaeda and they had very significant details about exactly how they would carry out the attack, where they would carry it out -- that's what makes it sound so plausible," Rep. King said.

The NYPD and Metropolitan Transportation Authority said they were on high alert and adding extra manpower. Even before the threat became public Police Commissioner Ray Kelly said he was adding more cops.

"We always have to be concerned when we have large gatherings like on Thanksgiving," Kelly said. "We always have to have sufficient deployment of police officers."

New Yorkers had this reaction to the new threats.

"I've got to get on a train, but that's horrible," commuter Carolyn Tobin said. "I mean ... the memory ... but just like after 9/11, we just kept going on."

Added Ryan Barreiro: "I'm not too worried about it. That's exactly what they want. If they're gonna get you, they're gonna get you."

"I'm not afraid," Rick Hendrickson said. "I've lived here my whole life, in Manhattan, so has my wife and we just take life as it comes along."